The present invention relates to an online roll grinding method and an online roll grinding apparatus for grinding the surfaces of working rolls during rolling operation of a rolling mill.
Generally, working rolls of a rolling mill during rolling of a plate are worn at only rolling portions thereof with the result of steps formed between the rolling portions and non-rolling portions of the working rolls, and, therefore, a rolling system has been adopted which is limited in that the rolling schedule must be from wider rolling stocks to narrower rolling stocks. Besides, the life of the working roll has been determined in consideration of the influences on product quality of formation of the steps and variations in roughness of the working roll surfaces due to rolling. Due to the life of the working rolls determined in this manner, the number of rolling stocks which can be rolled by use of the same working rolls has been restricted.
On this account, there has hitherto been proposed an online roll grinding apparatus such as described in Japanese Patent Publication No. 2708351. This apparatus eliminates the above-mentioned schedular limitation on the rolling system (from wider rolling stocks to narrower rolling stocks) to thereby achieve schedule-free rolling, and prevents the formation of working roll steps between rolling portions and non-rolling portions to thereby provide the working rolls with a uniform surface roughness, leading to a prolonged working roll life. Accordingly, the number of rolling stocks which can be rolled is increased, and the unit of working rolls is reduced. Thus, the apparatus is aimed at energy conservation, improved product quality and enhanced productivity.
According to the above-mentioned Japanese Patent Publication No. 2708351 xe2x80x9cROLLING MILL, ROLL GRINDING APPARATUS AND ROLLING METHODxe2x80x9d, an online roll grinding apparatus comprises at least one grindstone device for each of upper and lower working rolls, and grinding is carried out while moving the grindstone device along the longitudinal direction of the working rolls over the entire length of the rolls. In the known example, there is no definition as to the moving direction during grinding of the grindstone devices disposed respectively for the upper and lower working rolls. Generally, for ease of control, during grinding the upper and lower grindstone devices are both moved along the longitudinal direction of the working rolls in the same direction, namely, either from a draft operating side (hereinafter referred to as xe2x80x9coperating sidexe2x80x9d) toward a rotationally driving side (hereinafter referred to as xe2x80x9cdriving sidexe2x80x9d), or from the driving side toward the operating side.
On the other hand, Japanese Patent Laid-open No. Hei 11-197721 discloses online roll grinding in which a grind grain with an angle of intersection relative to the circumferential direction of working rolls is provided for enhancing efficiency of grinding, wherein the directions of the grind grain pattern with the angle of intersection are determined to be symmetrical within the longitudinal direction of the working rolls, between the upper and lower working rolls, and between adjacent stands. By such grinding, frictional forces generated between the rolling stock and the working roll in the width direction are canceled, whereby meandering of the rolling stock is prevented.
In the online grinding apparatus disclosed in the above-mentioned Japanese Patent Publication No. 2708351, when the upper and lower grindstone devices for grinding the working rolls in the longitudinal direction are both moved in the same direction, namely, either from the driving side toward the operating side or from the operating side toward the driving side, there arises a difference of working roll surface roughness such that the ground portions of the working rolls have smaller surfce roughness and unground portions of the working rolls have larger surface roughness, along the longitudinal direction of each working roll and between the upper and lower working rolls upon grinding.
The difference in the surface roughness of the working rolls causes a variation in frictional coefficient in the longitudinal direction of the working rolls at the time of rolling. Because the number of the working rolls during grinding by the online roll grinding apparatus is two (upper one and lower one), the variation in the frictional coefficient is doubled. Due to the difference in the frictional coefficient generated in the width direction of the rolling stock and between the working roll surfaces upon rolling, the rolling stock meanders and there arises drawing (squeezing) or bad shape (end elongation, middle elongation) due to meandering. As a result, product quality is lowered, productivity is lowered, and the merit of the online roll grinding apparatus is reduced.
When rolling is carried out using working rolls which have preliminarily been ground before rolling according to the technique disclosed in the Japanese Patent Laid-open No. Hei 11-197721, frictional forces generated in the width direction of the rolling stock are canceled, and meandering of the rolling stock is prevented effectively. However, this known example also does not define the moving direction of the grindstone devices during grinding of the working rolls. It has been known that, when grinding is carried out by moving the upper and lower grindstone devices in the same direction during pass rolling by rotation of the working rolls, a difference in frictional force is generated in the width direction of the rolling stock, resulting in meandering of the rolling stock and attendant bad shape. Therefore, the technique of the known example permits grinding only during intervals of rolling, and is unsuitable for application to grinding during pass rolling.
Accordingly, it is an object of the invention to provide an online roll grinding method and an online roll grinding apparatus by which the difference in frictional coefficient in the longitudinal direction of working rolls due to grinding is reduced so that meandering of a rolling stock at the time of grinding during pass rolling is prevented, thereby preventing drawing (squeezing) of the rolling stock or bad product shape due to meandering, lowering of product quality and lowering of productivity. (1) In order to attain the above object, according to the invention, there is provided an online roll grinding method using at least one upper-side roll grindstone device and at least one lower-side roll grindstone device faced respectively to an upper-lower pair of working rolls to grind surfaces of the working rolls being rotated, and a moving device for moving the upper-side roll grindstone device and lower-side roll grindstone device along the axial direction of the working rolls, wherein grinding is carried out while moving the upper-side roll grindstone device and the lower-side roll grindstone device in reverse directions during rolling.
By this, grinding directions for the upper and lower working rolls are set in reverse relationship, namely, for example, the upper-side roll grindstone device is moved from the driving side toward the operating side while the lower-side roll grindstone device is moved from the operating side toward the driving side. Resultantly, the difference in frictional coefficient in the longitudinal direction of the upper and lower working rolls can be reduced even in online roll grinding carried out during pass rolling, whereby drawing (squeezing) of the rolling stock and bad product shape due to meandering can be obviated, and product quality and productivity can be enhanced. (2) In an online roll grinding method as set forth in (1) above, preferably, grinding by the upper-side roll grindstone device during rolling and grinding by the lower-side roll grindstone device during rolling are started simultaneously from opposite sides, and the moving velocity of the upper-side roll grindstone device and the moving velocity of the lower-side roll grindstone device are controlled to be equal to each other.
By this, the difference in frictional coefficient in the longitudinal direction of the upper and lower working rolls can be reduced stably. (3) Further, in order to attain the above object, according to the invention, there is provided an online roll grinding apparatus comprising at least one upper-side roll grindstone device and at least one lower-side roll grindstone device faced respectively to an upper-lower pair of working rolls to grind surfaces of the working rolls being rotated, and a moving device for moving the upper-side roll grindstone device and lower-side roll grindstone device along the axial direction of the working rolls, wherein a movement controlling device is provided for controlling the moving device so as to move the upper-side roll grindstone device and the lower-side roll grindstone device in reverse directions during rolling.
By this, the difference in frictional coefficient in the longitudinal direction of the upper and lower working rolls can be reduced even in online roll grinding carried out during pass rolling, whereby drawing (squeezing) of the rolling stock and bad product shape due to meandering can be obviated, and product quality and productivity can be enhanced. (4) In an online roll grinding apparatus as set forth in (3) above, the movement controlling device controls the moving device so that grinding by the upper-side roll grindstone device during rolling and grinding by the lower-side roll grindstone device during rolling are started simultaneously from opposite sides, and that the moving velocity of the upper-side roll grindstone device and the moving velocity of the lower-side roll grindstone device are equal to each other.
By this, the difference in frictional coefficient in the longitudinal direction of the upper and lower working rolls can be reduced stably.
The above and other objects, features and advantages of the present invention will become apparent from the following description and appended claims, taken in conjunction with the accompanying drawings which show by way of example some preferred embodiments of the invention.